CURRENT LITERATURE 
BOOK REVIEWS 
Heredity as an exact science 
Problems of evolution have taken a dominant place in biology ever since 
the appearance of DARwIN’s Origin of species. During the latter part of the 
last century there was little important progress made, though there was an 
abundance of academic discussion and repeated analysis of data recorde1 by 
Darwin and a few other observers ; but already in the closing years of the 
century a reaction had set in. With the beginning of the present century this 
reaction reached its first important expression with the appearance of DE 
RIES’S Mutationstheorie, which marked the beginning of a new epoch in the 
study of the various factors of evolution, an epoch not inappropriately called 
the “era of experimental evolution.” Other branches of biology have exhibited 
at the same time a corresponding development. Instead of pure speculations, 
and of generalizations from observations uncontrolled by experimental on 
tions, there has been a swiftly growing demand for greater exactness in observa- 
tions and for experimentation. . 
As an essential part of the reaction, the development of mathematical 
methods by Professor Kart PEARSON and a few others promised for a ime si 
key to the riddles of evolution. This movement, led by a pure mathematician, 
developed a series of beautiful methods for the mathematical analysis of oat 
and the comparison of variations. These methods are of the greatest oe 
tance when rightly used, but owing to the almost invariable lack of an equa : 
keen biological analysis, the applications of these methods have led to — 
spurious product, whose showing of depth and accuracy has been mae a 
because the methods are faulty, but because of their application as a - 
which did not supply the one fundamental assumption of homogeneity UP® 
which the whole biometrical system is based. ise 
Parallel with this movement toward the use of mathematically SS ae 
methods, there has been a rapidly increasing utilization of pedigree ee 
genetic methods involved in efforts to distinguish between mutations 4° tress 
tuations, and in Mendelian investigations in heredity, which methods ae bio- 
chiefly upon biological analysis. The antagonism of active workers WIL" 
and genetics. On the one hand were the mathematical writings of me ae 
PEARSON and a number of his students, in which mathematical met) 
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